1. Field of the Invention
The invention relates to the alteration of the composition of gas supplied to an enclosed space and is particularly applicable to aircraft.
An example of an enclosed space which requires gases of differing compositions is the space formed by the passenger and crew carrying zones of an aircraft. In commercial aircraft, air for passengers in the cabin and for the crew in the flight deck is derived from a source external to the cabin and flight deck. In order to reduce the requirement for air from such an external air supply, an air re-circulation system is commonly provided in which air from the flight deck and cabin is taken, filtered and cooled and then returned to the cabin and the flight deck, often with the addition of a small proportion of fresh air. The air from the cabin and flight deck contains significant quantities of carbon dioxide and water vapour. In order to reduce the volume of carbon dioxide and water vapour in the recycled air, a proportion of the recycled air is passed through a pressure swing adsorption system which removes carbon dioxide and water vapour and returns the carbon dioxide and water vapour depleted air to the remainder of the recycled air, which is then returned to the cabin and flight deck.
2. Brief Review of the Prior Art
Suitable pressure swing adsorption systems are well known and are described, for example, in EP-A-0332390.
There is also a requirement in aircraft for a supply of oxygen in emergency in the event of cabin and/or flight deck depressurization. This is achieved by the use of a separate system including masks for the passengers and the flight deck crew supplied from a separate source of oxygen. For example, there are available candles which on combustion release oxygen.
An alternative is disclosed in U.S. Pat. No. 4,428,372 where a pressure swing adsorption system takes engine bleed air, increases the oxygen content of the air by the adsorption of nitrogen and then supplies the oxygen-rich air to an amergency oxygen supply system. Some oxygen-rich air from the pressure swing adsorption system is supplied to a storage tank and is drawn from the tank in the event that there is an interruption in the supply of oxygen-enriched air from the pressure swing adsorption system.